Graphical Detection Method for Delaminations
In this paper, a simple graphical method for the detection of delaminations in damaged composite laminates is introduced. By using this method, both delamination size and location can be predicted accurately. First, a frequency database for the damaged beams with a range of delamination sizes and locations is generated using a Finite Element (FE) model; then for each mode, a surface plot relating the delamination size, location and frequency shift is generated. The next step is to look up the actual frequency shift (either from numerical simulation or experiment) from surface plots relating to three or more modes to get the intersection curves, which show the possible combination of delamination size and location for each mode. Finally the intersection curves of different modes are plotted together and the intersection point of all the curves indicates the possible delamination size and location, where the frequency shifts for all the modes can be matched. We demonstrate that this method is able to predict both delamination size and location fairly accurately. This method can be expanded to detect the propagation of delaminations by only monitoring the shifts in natural frequencies. It has the potential to detect multiple delaminations through continuous monitoring, provided that they do not occur simultaneously. This method has promising applications in the Structure Health Monitoring (SHM) of composite structures.
Z. F. Zhang et al., "Graphical Detection Method for Delaminations", Applied Mechanics and Materials, Vols. 66-68, pp. 1410-1415, 2011